Hello,
I am trying to learn some basics of mainframe performance,
There was a term "velocity" allocated to workloads,
The manual says,
Velocity: This is a measure of how fast work should run when ready, without being delayed for resources. Velocity is a percentage from 1 to 99.

The formula for velocity is:

Velocity = (# Using Samples * 100) / (# Using Samples + # Delay Samples)
Could you please let me know what is the meaning of "samples" in the above citation.

Job X is running in an address space. Out of the first 100 times WLM samples while job X is executing, job X is using CPU on 43 of those and waiting (for I/O, for example) for 57 of them. The velocity will be 43. Velocity is basically a measure of how active the job / service class / TSO user / ... is within the system.

Velocity is used in setting goals for WLM -- service class PRDBATMD for example may have a velocity goal of 20. This means all jobs executing in that service class (whether 1 or 40) will have WLM attempting to give 20% of the processing time to them.

A couiple of notes to keep in mind while looking at WLM:
1. WLM is goals; PI (Performance Index) measures how well WLM is doing at achieving those goals
2. WLM performance is really only effective when CPU is 100%; if the CPU utilization is 80% then the address spaces on the system are not using all the CPU anyway.

There may still be a few sites running very old releases of z/OS or OS/390, in which case they may not be using WLM goal mode. However, since z/OS 1.3 the use of WLM has not been optional -- the old method of setting up performance groups and domains via IEAICSxx AND IEAIPSxx won't work with WLM goal mode.

WLM is present in all releases of z/OS as well as some releases of OS/390 (IIRC), so it has been around a while. As far as I know, there are no competitor products (although I've never looked) especially since WLM is available for all z/OS systems anyway. And setting up goals under WLM with the ISPF panels is much easier than translating performance metrics into IEAICSxx AND IEAIPSxx parameters.